Where do I put a tone control in this schematic?

[Mr.Kite]

Hi guys, it's been a while since my last visit here...I'm glad to be back!

I found a couple of "JOP" (JFET Operational Amplifier) modules created by an old Italian electronic magazine and I've breadboarded the "basic" distortion circuit shown on the magazine: https://www.robertobizzarri.net/NE/sommario.php?p=236

Just click on the pdf link and go to page 44-45: I'm interested in the "upper" part around the big yellow IC1 (the "JOP" module), let's forget about the "PLL" section...

The circuit runs at 18V and the distortion character\touch response is very "amp like", but the switches are not that useful, and I'd like to add a passive tone control instead, like the first one shown here: http://www.muzique.com/lab/swtc.htm

I tried it inserted between C13 and R3, and it works, although it sucks a tiny bit of volume.

My question is: there are better places or better low loss passive tone circuits to try? If not, should I add coupling caps before\after the tone control?

Thanks in advance,


MrKite

[PRR]

> it's been a while

We were wondering....

Without knowing the details of the JOP, I see the output is a 100k:10k divider, and begs to be replaced with a lossy tone control of your choice.

No idea what the rest of all that does.

[anotherjim]

My guess is the JOP is a 4 stage class-A JFET amplifier module. It directly feeds a separate clean output and also the PLL circuit.
The PLL idea we have seen before. The binary counter in the loop providing 4 octave related harmonics that in this case are output via the organ style diode gate/VCA set according to the direct signal envelope out of IC4d and the mixer controls.
Personally, I don't think a passive filter will do it justice. I would add a simple synth type voltage-controlled active filter to output and control it with the VCA envelope and a CV tuning pot. Escobedo's Quick & Dirty filter for instance.

[Mr.Kite]

We were wondering....

Funny. The rudeness on this forum is proverbial, maybe that's why I don't spend a lot of time here...

Anyway, could you please be more accurate\helpful and less ironic?

I'm not sure about your advice: which components (R2, R4...?) would you eliminate and where and what components would you add? Do I need coupling caps before and after the tone control in your opinion?

I would be grateful if you could be a little more specific, thanks...

[Mr.Kite]

My guess is the JOP is a 4 stage class-A JFET amplifier module.

Yep. But I'm building just the "core" distortion circuit for now, just the "upper" part of the schematic: IN -> JOP module -> OUT, and I would like to add a tone control...I'm open to suggestions, thanks for your help!

[abram]

thanks for posting this circuit! i'm into the PLL design with separate harmonic controls. i'd be interested to hear the whole thing.

probably the easiest thing to do in your case would be to pick one of the tone controls shown on the SWTC page to put after C13. you might need to reduce the value for R2 if not do away with it entirely and just connect C13 directly to pin 9. as PRR mentioned, the passive tone controls are a bit lossy. i've done a number of Mitsumin vavlecaster builds, and the tone control for that circuit seems to work pretty well for how simple it is (C3 here would be C13 in your schematic). might be worth a try.

[Mr.Kite]

might be worth a try.

Thanks! Let's see what happens with this simple control...

The concept behind the PLL sounds interesting, but my experience with Nuova Elettronica's kits for guitar effects\musical gear in general isn't always positive: they were more "electronic guys" than musicians, their circuits are a good bases to experiment, but they're not very "fine tuned" for musical applications.

For example, S2-S5 are switches which engage different caps to increase the gain (all frequencies) or just the high frequencies: cool idea, right? Unfortunately the pedal is already pretty gainy and bright sounding (that's why I want a tone control), and the values are too big and too small: the 220uF caps increase the gain too much, both together sounds interesting for "special effects", but not very musical: gated, sputtery and very nasty, unbearable. While the 22\10nF caps are too small for guitar frequencies, boosting above what a typical guitar speaker can reproduce.

I found that two ~100uF (or just one 220uF in the first stage only) boost the gain more than enough, and that ~2,2uF are much more suitable for boosting presence\treble (and some mids) with a guitar (or bass) speaker...

[abram]

I found that two ~100uF (or just one 220uF in the first stage only) boost the gain more than enough, and that ~2,2uF are much more suitable for boosting presence\treble (and some mids) with a guitar (or bass) speaker...

not a problem! i did notice a lot of RF stuff scattered through out the issue, so that makes total sense.

i'm not sure what kind of JFETs you've used with your designs, but all the ones i've ever done any audio work with (only J201s and MPF102s) have all seemed pretty bright to me as well. i could definitely see those source bypass cap values requiring a bit of tweaking to get right. hopefully, that high frequency roll-off will help.

[PRR]

The rudeness on this forum is proverbial

I am sorry if I offended. That was not my intent. I will try not to do it again.

[Mr.Kite]

I am sorry if I offended.

No, you didn't. It's just a bit weird the humor around here sometimes...let's forget about it.

[anotherjim]

In the JOP, is the cap C9 in the middle an interstage coupling? In which case, a tone control could go in series there.

[Mr.Kite]

I tried the tone control posted by Abram, but I had to use very different values to get something effective: 5-10k linear pot and 0,1uF cap.

It sounds better (more "natural"?) in series with C9, as anotherjim suggested: it sucks some volume but not that much. Now it works similar to the "presence" control on a Marshall amp, quite effective and "neutral" sounding around the 12 o' clock position, or a little above.

I'm quite happy with the result, but I'd like to regain some overall brightness\volume: I could make the tone switchable, and\or add the right value cap to the S2\S3 switch to boost some highs, but what's the purpose of the R2-R4 resistors? Maybe they serve to set the output impedance? There's a way to manipulate the output level to regain some dBs without significantly alter the output impedance by tweaking those values?

Thanks in advance, and sorry if these are trivial questions, but I'm pretty new to the whole thing...

[Mr.Kite]

In the JOP, is the cap C9 in the middle an interstage coupling?

Yeah, I think so. The tone control works.

I really don't know much about the JOP mudule, it's all gooped. You can see a drawing of the actual device at page 39 of the magazine that I posted in the first link.